xml has a definition file which can be used to validate that your tags are correct.
Both the formats are well supported for parsing so I guess you can go with which ever, although in the industry, xml is often favored.
Joined: May 10, 2011
The approach will depend on what you want. In general I have used JSON because it's smaller and more readable than XML.
Just for note, Twitter and Foursquare left XML and started using exclusively JSON.
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